The normal anatomy of the spinal column presents different alignment and rotational characteristics along three spatial planes. In the coronal (or frontal) plane, the vertebrae are normally aligned and present no rotation. In the transverse (or axial) plane, the vertebrae are likewise normally aligned and present neutral rotation. In the sagittal plane, the vertebrae present a certain degree of rotation and translation which form the physiological curvature of the spine; namely, cervical lordosis, dorsa or thoracic kyphosis, and lumbar lordosis.
Spinal deformities of varying etiologies are well known. Such deformities include abnormal spinal curvatures, such as, for example, scoliosis, kyphosis, and/or other abnormal curvatures wherein natural alignment of the spine is altered. With specific regard to scoliotic deformities, the abnormal curvature of the spinal column is three-dimensional. Specifically, scoliotic deformities can be separated into abnormal translation and/or rotation of the vertebrae in each of the coronal, transverse and sagittal planes. Therefore, treatment of scoliosis should preferably be aimed at addressing reduction of the abnormal curvature in each of the three spatial planes.
A number of methods and techniques have been used to reduce abnormal spinal curvatures. Most of these techniques have been based on anchoring devices onto posterior elements of the spine (e.g., via clips or wires). Such techniques reduce the translational aspects of the deformity, but have little or no effect on the rotational aspects.
Additionally, pedicle screws have been used in the treatment of scoliosis, thereby raising the possibility of derotation of the spinal column. However, techniques for treatment of scoliosis using pedicle screws are based essentially on translation to align the spinal column, either by bending or rotating a spinal rod after the rod is engaged to the screws, or by forcing the pedicle screws into engagement with the rod. Other reduction techniques provide for derotation via the use the pedicle screws, but such derotation is usually implemented following placement of the spinal rod individually and consecutively into engagement with the pedicle screws. Additionally, when pedicle screws are anchored to a scoliotic spine, the screws follow the curvature of the spine and tend to be inclined in the transverse plane depending on vertebral rotation, thereby complicating placement of the spinal rods.
Treatment of a spinal deformity via a reduction technique to address both the alignment and rotational aspects of the deformity along all three spatial planes would be desirable. Thus, there remains a need for improved instrumentation and methods for reducing spinal deformities. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.